FELICIA in the cold weather chuggs a bit, hesitates, lumpy tickover. now the weather is warm it has become smooth, which sensor has failed?

the little gate in the air box?

Yes possibly, how to test easily is the question?

or the coolant temperatute sensor

No fault codes present.

there doesn't necessarily have to be any faults for there to be a problem, so long as the sensor is within an acceptable range it just thinks that everything is normal

air gate test: hair dryer and freez spray.

If it's a 1.3 check the valve clearances. If they are tight you will get those symptoms from a cold start.